Digital Fluoroscopic Imaging - AAPM

[Pages:50]Digital Fluoroscopic Imaging:

Acquisition, Processing & Display

J. Anthony Seibert, Ph.D. University of California Davis

Medical Center Sacramento, California

Outline of presentation

? Introduction to digital fluoroscopy ? Digital fluoroscopy components ? Analog and digital image characteristics ? Image digitization (quantization/sampling) ? Image processing ? Summary

1

History of digital fluoroscopic imaging

? ....... mid 1970's

? Modified II/TV system with "fast" ADC ? Temporal and energy subtraction methods

? ....... 1980's

? Clinical DSA angiography systems ? Qualitative and quantitative improvements ? Image processing advances ? Temporal and recursive filtering

History of digital fluoroscopic imaging

? ....... 1990's

? Quantitative correction of image data ? Rotational fluoroscopic imaging ? Micro-fluoroscopic imaging capabilities ? CT fluoroscopy (using fan-beam scanners) ? Cone-beam CT reconstructions

? ....... 2000 - present

? Introduction of real-time flat-panel detectors

2

Why digital fluoroscopy / fluorography?

? Low dose fluoroscopic imaging (digital averaging, last frame hold)

? Pulsed fluoroscopy and variable frame rate ? DSA and non-subtraction acquisition and display ? Digital image processing and quantitation ? Image distribution and archiving, PACS

? Introduction to digital fluoroscopy ? Digital fluoroscopy components ? Analog and digital image characteristics ? Image digitization (quantization/sampling) ? Image processing ? Summary

3

Fluoroscopic Acquisition Components

Side View: C arm System

TV Camera

C-Arm Apparatus

Image Intensifier

Collimator X-ray Tube

TV Monitor

Peripherals

Cine Camera Photospot Camera Spot Film Device Digital Photospot DSA System

Image Intensifier - TV subsystem

Input phosphor Photocathode (- )

e-

Housing

Focusing electrodes

Aperture (Iris)

Evacuated Insert

Anode (+)

TV camera

Lens optics and mirror assembly

e-

X-rays in

Grid

Output phosphor

~25,000 Volts acceleration

e-

e-

ee-

Video or CCD camera to ADC to Digital Image

Light out Recorder

CsI input phosphor

e-

e- ee-e-

SbCs3 photocathode

X-rays Light Electrons

ZnCdS:Ag output phosphor

Electrons Light

~5000 X amplification

4

Structured Phosphor: Cesium Iodide (CsI)

Crystals grow in long columns that act as light pipes

CsI

Light Pipe (Optical

LSF

Fiber)

TV camera readout and output video

5

TV camera specifications

? Low resolution:

? 525 line, interlaced, 30 Hz (RS-170)

? High resolution:

? 1023 - 1049 line, interlaced, 30 Hz (RS-343)

? Highest resolution

? 2048 line systems

? Progressive scan a must for short pulse-width digital applications

II-TV digital systems

? Two decades+ of availability ? Video signal is convenient for digitization ? Low noise performance of II's: SNR ? Well-developed capabilities

? IA, DSA, digital photospot ? Rotational CT

? CCD camera implementations ? II is Big and bulky; image distortions prevalent

6

Flat-panel Fluoroscopy / Fluorography

? Based upon TFT charge storage and readout technology

? Thin-Film-Transistor arrays

? Proven with radiography applications ? Just becoming available in fluoroscopy

? CsI scintillator systems (indirect conversion) ? a-Se systems (direct conversion)

Photodetector: a - Si TFT active matrix array

Scintillator

Photodiode: Light to electronic signal

X-rays to light

Amplifiers ? Signal out TFT: Storage and readout

7

Amorphous Silicon

TFT active matrix array

Amplifiers ? Signal out

Gate

G1

switches

Active Area

Dead

Thin-Film G2 Transistor

Zone

Storage

Fill Factor = Active area ? (Active area + Dead ZoGn3e) Capacitor

Large pixels: ~ 70% Small pixels: ~ 30 %

Data lines

D1 CR1 D2 CR2 D3

Charge Collector Electrode CR3 Charge Amplifiers

Analog to Digital Converters

Amplifiers ? Signal out

Amorphous Silicon

TFT active matrix array

G1 Expose to x-rays

G2

Store the charge

G3

Active Readout Activate gates Amplify charge Convert to Digital

8

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